The invention relates to a diagnostic device for detecting a layer boundary in an eye, a lens or another translucent body, with a light source, wherein the light source defines an object plane, with a sensor unit, with a beam path which is designed to guide at least one measuring beam of the light source from the object plane of the light source into an image plane and/or into an intersecting region of the measuring beam with an optical axis in the eye, with an actuator designed to move the image plane and/or the intersecting region along the optical axis, wherein the beam path is designed such that, in a detection state, the measuring beam is guided from a layer boundary of the eye into the sensor unit if the image plane and/or the intersecting region is located on the layer boundary, and with an evaluation unit designed to recognize the detection state on the basis of the signals of the sensor unit. The invention also relates to a ring element for the diagnostic device.
For the treatment of the human eye, for example when performing cornea corrections using laser beams, precise information on the inner structure of the eye is required. In many areas of application, information about the eye is combined into a 3D eye model. The cornea of the eye, being the foremost layer of the eye, is of particular importance for modeling. The corneal thickness, for example, is of relevance for correcting the intraocular pressure as measured by tonometry, since the value of the intraocular pressure as measured by commonly used methods depends on the corneal thickness.
A pachymeter (sometimes also called a pachometer) is a measuring instrument for measuring the corneal thickness of the human eye. The pachymeters known in the art are based on different measurement techniques:
One implementation of a pachymeter on the basis of non-contact optical measurement involves a measurement technique called OLCR (optical low-coherence reflectometry). Another implementation which, however, requires contact is the determination of the corneal thickness using ultrasound, for which a small ultrasound probe is placed on the cornea. In principle, both implementations allow for the determination of corneal thickness, anterior chamber depth, intraocular lens thickness and eye length to a precision of a few micrometers. Another way of measuring the anterior part of the eye is to combine a slit lamp with a Scheimpflug camera. This measuring instrument assembles the 3D image of the eye from several individual measurements where the eye is measured in several layers and the Scheimpflug camera takes a picture of each sectional plane.
All three measurement techniques have their weaknesses due to their working principles. Ultrasound measuring instruments, for example, have the disadvantage that they need to be placed full-contact on the eye, a procedure only a skilled expert can carry out in a reproducible way. The system comprising a Scheimpflug camera and a slit lamp is comparatively large, which makes it difficult to integrate into a treatment laser, for example. The measuring instruments based on the OLCR technique can usually only measure distances within the visual axis of the eye.
The aim of the present invention is to propose a diagnostic device for detecting a layer boundary which facilitates the determination of layer thicknesses in the human eye. A further aim of the present invention is to present a special optical element for said diagnostic device.
A diagnostic device for detecting a layer boundary in an eye, a lens or another translucent body is proposed within the scope of the invention. In particular, one or several layer boundaries in the region between the cornea and the lens in the anterior part of the eye can be detected. Said anterior part of the eye contains the cornea, the anterior chamber and the lens. Some layer boundaries which are possible to detect are the following:    a) layer boundary: external side of the cornea    b) layer boundary: cornea—anterior chamber    c) layer boundary: anterior chamber—lens    d) layer boundary: lens—vitreous body.
The diagnostic device is preferably designed as a pachymeter which is used to measure the corneal thickness of the human eye, among other things. In alternative fields of use it is also possible to measure other translucent bodies, e.g. lenses, in particular contact lenses.
The diagnostic device comprises a light source, said light source being preferably designed as a laser source or a light-emitting diode, in particular a superluminescent diode. The light source defines an object plane, wherein the object plane may be located at the position of the light source or at an intermediate image of the light source.
The light source facilitates the emission of at least one measuring beam, in particular a measuring laser beam, which can be bounced back, in particular reflected, from one or several layer boundaries in the eye. The wavelength of the light source is preferably in the visible spectrum, meaning e.g. between 400 nm and 650 nm.
As a further component, the diagnostic device comprises a sensor unit designed for detecting the at least one measuring beam.
A beam path serves to guide and optionally shape the at least one measuring beam from the object plane of the light source into an image plane and/or into an intersecting region of the measuring beam with an optical axis in the eye. The optical axis may correspond, for example, to a symmetry axis of the beam path but can also be selected arbitrarily. Through the beam path, the light source (or an image thereof) is projected into the image plane and/or the intersecting region, with the projection being a real image of the light source and/or a measuring point formed by the light source.
The diagnostic device has an actuator which is designed to move the image plane and/or the intersecting region along the optical axis. With the actuator, it is thus preferably possible to influence the beam path such that the focal position and/or the lateral position of the measuring beam in the eye is changed, which makes at least a movement of the image plane and/or the intersecting region along the optical axis possible.
Furthermore, the beam path is designed such, in a detection state, the measuring beam is guided from a layer boundary in or on the eye into the sensor unit if the image plane and/or the intersecting region is located on the layer boundary. The actuator thus serves to vary the condition of incidence of the measuring beam onto and/or into the eye until the detection state is reached, said detection state being a state where the measuring beam is guided from the layer boundary through the beam path into the sensor unit as a directed or diffuse reflection.
As a further component, the diagnostic device has an evaluation unit designed to recognize the detection state on the basis of the signals of the sensor unit.
To summarize, a detection state with regard to a layer boundary is detected if and only if the measuring beam is guided back into the sensor unit. The detection on the basis of the signals of the sensor unit can be performed, for example, by using the position of the returning measuring beam, the intensity of the returning laser beam etc.
Within the scope of the invention, it is proposed to estimate and/or determine a layer thickness between a first and a second layer boundary on the basis of the position of the actuator in a detection state of the first and the second layer boundary.
It is therefore an idea of the invention to operate the actuator such that the detection state of a first layer boundary is detected and the position of the actuator is recorded. In a further step, the detection state of a second layer boundary is detected and again the position of the actuator is recorded. Since the beam path is known, it is now possible to estimate and/or determine the distance between the two layer boundaries and hence the layer thickness between the layer boundaries. In this context, the term “estimate” relates to a procedure to be followed if not all required parameters of the beam path and/or the eye are sufficiently known and, for example, estimated parameters have to be used. If all parameters are sufficiently known, the layer thickness can be determined, in particular calculated precisely, using these parameters.
In a first possible embodiment of the invention, the beam path is designed such that an image of the light source can be projected into the image plane in the eye. In particular, the measuring beam is expanded within the beam path, which means that it is guided, at least in sections, with a beam diameter, in particular an outer beam diameter (FWHM), larger than 3 mm, preferably larger than 5 mm. The actuator is preferably designed as an adaptive optical element, such as an adaptive lens, in particular a fluid lens, and/or as a movable optical element, in particular a slidable optical element, such as a slidable lens. In particular, the beam path is designed such that the measuring beam on its way to the eye overlaps with itself on its way back to the sensor unit in the region between the eye and the first optical element. In this embodiment, the diagnostic device is designed similar to a confocal microscope, with the detection state being reached precisely when the image plane is located on the layer boundary and thus a confocal lighting condition exists.
In another embodiment of the invention, the measuring beam is propagated, at least in sections, in an unexpanded way, and in particular only a single measuring laser beam is employed. Between the light source and the eye, and in particular between the last optical element and the eye, said measuring beam, being unexpanded, has a diameter (FWHM) which is always smaller than 2 mm, in particular smaller than 1 mm. It is particularly preferred in this embodiment that the actuator is designed as a scanning means, in particular as a 2D scanning mirror. By way of the scanning means, the measuring beam can perform scanning of the eye in the depth direction along the optical axis and laterally e.g. linear scanning and/or scanning of the entire surface, thus reaching the detection state. In the detection state the individual measuring beam is preferably guided back to the sensor unit on a different beam path, in particular between the eye and the adjacent optical element.
What both embodiments have in common, however, is that the measuring beam can be guided back via the eye, in particular via the layer boundary, into the sensor unit and the evaluation unit can recognize the detection state on the basis of the signals of the sensor unit only in certain positions of the actuator.
To achieve sufficient measurement accuracy it is possible, for example, to arrange a spatial filter and/or an aperture in the beam path in front of the sensor unit, wherein said spatial filter and/or aperture ensures that the measuring beam can be guided back onto the sensor unit only in the detection state with sufficient measurement accuracy.
Another possibility is to design the sensor unit as a unit with spatial resolution, in which case the sensor unit may be designed, for example, as an image capture chip, such as a CMOS chip or a CCD chip, or as a position sensitive diode (PSD). In these embodiments, detection can be achieved by having the evaluation unit interpret the position and/or intensity of the returning measuring beam with regard to the detection state.
In a particularly advantageous embodiment of the invention, the beam path is designed such that the measuring beam for detecting the layer boundary is restricted to one ring area or a smaller area on at least one optical element, in particular the last optical element in front of the eye, thus leaving a central region, in particular an aperture region, uncovered. The reasoning for this arrangement is the observation that using an outer region is sufficient for detecting the layer boundary, so that the central region can be left uncovered for other measuring and/or control beams. In particular, it is possible to arrange an optical element in the central region that is different from the optical element in the ring area or the edge area.
Preferably, the ring area has an optical component, in particular designed as a ring element, which guides the measuring beam onto the image plane and/or onto the intersecting region and which is designed as a diffractive optical element and/or a diffractive element and/or a reflecting element. Particularly preferably, the optical component is implemented such that the intersecting region is moved along the optical axis by changing the radial position of the measuring beam passing through in relation to the optical axis.
In a further form of the invention, the optical component has several regions in the direction of rotation around an or the optical axis, said regions guiding the measuring beam into different regions, in particular depth regions, along the optical axis. This embodiment is based on the consideration that there is regularly a distance larger than 5 mm between the first possible layer boundary, which is located between the surrounding area and the cornea, and the last possible layer boundary, which is located between lens and vitreous body. To achieve a sufficiently high measurement accuracy, such as better than 20 micrometer, preferably better than 10 micrometer, the different regions are arranged in the direction of rotation, said regions guiding the measuring beam into different regions along the optical axis. A first region thus guides the measuring beam into the region of the cornea, another region guides the measuring beam, for example, into the region of the lens, etc.
In an advantageous further form of the invention, the beam path is designed such that accommodation beams can be sent through the central region of the ring area, said accommodation beams forming an accommodation target in the eye. For example, a regular lens is arranged in the central region, said lens guiding or shaping the accommodation beams. The accommodation target provides a stimulus to the eye to fixate in a certain position with a certain prestressing of the lens, so that reproducible measurements of the layer thicknesses can be carried out.
In a possible further form of the invention, several accommodation targets may be formed which appear to the eye to be coming from different directions. The patient can be instructed during the diagnosis to fixate on the respective current accommodation target so that the eye of the patient is turned into a defined position. In this new position it is again possible to measure the layer thicknesses of the cornea etc., making it possible for the diagnostic device to generate a two-dimensional network of values measured for the layer thicknesses, depending on the number of accommodation targets.
In an advantageous embodiment of the invention, the accommodation beams and the measuring beams are created by the same light source. The light source has a dual function in this case, with the beams guided through the ring area being interpreted and used as measuring beams and the beams guided through the central region serving as accommodation beams for creating the accommodation target.
A further object of the invention relates to a ring element for a diagnostic device as described above or according to any one of the preceding claims, wherein the ring element has several regions in the direction of rotation, with pairs of said regions being assigned to a layer boundary of the eye.
In the following, the advantages of the invention will be shown with reference to the embodiments:
The main function of the diagnostic device is the non-contact measurement of layer thicknesses in the human eye. It is advantageous that the layer thicknesses of the eye can be measured in a defined state of the eye due to the optionally integrated accommodation target, said accommodation target putting the eye in a defined and reproducible state. The accommodation target can make an eye test character wander in the x and y direction as desired, and thus the eye to be measured can follow the eye test character. This makes it possible to turn the eye in all directions in a defined manner. It can also be provided, for example, that an observation camera records the rotation angle of the eye and the position of the eye, so that layer thicknesses can be measured at different positions and thus covering the entire surface. Due to its possible small size, in particular, the diagnostic device can be integrated in or combined with a topography measuring instrument and/or a wavefront measuring instrument. In this embodiment, the eye can be fully measured with a single diagnostic device. A 3D model of the eye can be created using the values measured by the diagnostic device, and said 3D model can then be utilised, for example, for correcting the refractive power in refractive surgery. Again because of its possible small size, the diagnostic device can be integrated into a treatment laser used for correcting the refractive power of the eye. The diagnostic device can measure the layer thickness of the cornea in situ and in real-time and monitor and control the results of the laser treatment.